QFusionStyle: de-pessimize arrow painting

Instead of holding three QPointF's in a QPolygonF, which will allocate
them on the heap, use QVarLengthArray<>, which will allocate them on
the stack instead.

Pick-to: 6.6 6.5
Task-numbber: QTBUG-112200
Change-Id: If078e5a9a5cb82fd03b511e28cceb88bd42996f8
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 2 insertions, 3 deletions

diff --git a/src/widgets/styles/qfusionstyle.cpp b/src/widgets/styles/qfusionstyle.cpp
index 95d0de8923..64a0b3c721 100644
--- a/src/widgets/styles/qfusionstyle.cpp
+++ b/src/widgets/styles/qfusionstyle.cpp
@@ -241,8 +241,7 @@ static void qt_fusion_draw_arrow(Qt::ArrowType type, QPainter *painter, const QS
         arrowRect.moveTo((rect.width() - arrowRect.width()) / 2.0,
                          (rect.height() - arrowRect.height()) / 2.0);
 
-        QPolygonF triangle;
-        triangle.reserve(3);
+        QVarLengthArray<QPointF, 3> triangle;
         switch (type) {
         case Qt::DownArrow:
             triangle << arrowRect.topLeft() << arrowRect.topRight() << QPointF(arrowRect.center().x(), arrowRect.bottom());
@@ -261,7 +260,7 @@ static void qt_fusion_draw_arrow(Qt::ArrowType type, QPainter *painter, const QS
         cachePainter.setPen(Qt::NoPen);
         cachePainter.setBrush(color);
         cachePainter.setRenderHint(QPainter::Antialiasing);
-        cachePainter.drawPolygon(triangle);
+        cachePainter.drawPolygon(triangle.data(), int(triangle.size()));
 
         QPixmapCache::insert(cacheKey, cachePixmap);
     }